1. Field of the Invention
The present invention relates to a heat transferable label and improved release composition therefor.
2. Description of the Prior Art
Prior art heat transferable labels for imprinting designs onto an article typically involve decorative laminates consisting of a paper base sheet or web coated with a wax or polymeric release layer over which a design is imprinted in ink.
U.S. Pat. No. 3,616,015 is illustrative of the prior art. In U.S. Pat. No. 3,616,015 a label carrying web such as a paper sheet includes a heat transferable label composed of a wax release layer affixed to a surface of the paper sheet and an ink design layer superimposed onto the wax release layer. In the heat transfer labelling process for imprinting designs onto articles, the label carrying web is subjected to heat and the laminate is pressed onto an article with the ink design layer making direct contact with the article. As the web or paper sheet is subjected to heat, the wax layer begins to melt so that the paper sheet can be released from the wax layer. After transfer of the design to the article, the paper sheet is immediately removed, leaving the design firmly affixed to the surface with the wax layer exposed to the environment. The wax release layer should not only permit release of the transferable label from the web upon application of heat to the web but also form a clear protective layer over the transferred ink design.
This commonly assigned patent discloses a wax release coating containing a modified montan wax which has been oxidized, esterfied, and partially saponified. In order to attain improved clarity of the transferred ink design the transferred wax coating over the ink design is subjected to additional heat processing after the label has been transferred onto an article. The additional processing involves postflaming, wherein the transferred wax coating is subjected to jets of high temperature gas either as direct gas flame or as hot air jets at temperatures of about 300.degree. F. to 400.degree. F. for a period of time sufficient to remelt the wax coating without substantially heating the bottle. Upon cooling of the remelted wax coating through use of ambient or forced cooled air, the cooled wax layer solidifies to form a clear, smooth protective coating over the transferred ink design. Although the heat transferable label and process disclosed in U.S. Pat. No. 3,616,015 represents an improvement over prior heat transferable labels, they are best suited to decoration of plastic articles which are not transparent. Although the heat transferable label disclosed in this reference may be utilized for decorating a wide variety of different plastics, there can be a degree of hazing or halo noticeable over the transferred label when the transfer is made onto clear plastic materials, despite use of postflaming. U.S. Pat. No. 3,616,015 is herein incorporated by reference.
U.S. Pat. No. 2,990,311 discloses a heat transferable decal having a release transfer layer composed of a mixture of a crystalline wax and a synthetic thermoplastic film-forming resin, principally an organic linear thermoplastic film-forming resin which is substantially water insoluble. The degree of compatibility of the resin and wax is controlled through selection and ratio of the components to give heat transfers of either the hot peel or cold peel type. In the hot peel transfer, the decal will adhere and release from the backing only immediately after application while the decal is still hot. In the cold peel transfer the transferred decal will adhere to the receiving surface when hot but will only release and transfer by peeling away the backing after the transfer has cooled. In either type of transfer, this reference teaches that resins and waxes (the latter being used for the release layer) should be mutually incompatible or insoluble at temperatures below the melting temperature of the wax such that the molten wax, upon cooling, will actually crystallize separately and distinctly from the resin. The resins are linear thermoplastic film-forming resins defined as essentially solvent-soluble, softened by heat and to involve only a minor amount or no cross-linkage.
Suitable resins specifically disclosed are polyvinyl acetate, polyethyl acrylate, polymethyl acrylate, polyethyl methacrylate, polypropyl methacrylate, polybutyl methacrylate, styrenebutadiene, acrylonitrile-butadiene, polychloroprene rubbers, polyvinyl butyral, ethyl cellulose, and polyvinyl acetate vinyl stearate copolymer (col. 5, 1. 38-44). The reference teaches that the wax component should be a material which derives its crystallinity mainly from the presence of long hydrocarbon chains and should melt over a relatively narrow range between the temperatures of about 50.degree. C. to 110.degree. C. The penetrometer hardness value (ASTM D5-52) when tested with 100 grams for 5 seconds at 28.degree. C. should be below about 15. Specific waxes disclosed as suitable are beeswax, candelilla wax, carnauba wax, hydrogenated castor oil, montan wax, paraffin wax, low molecular weight polyethylene, oxidized microcrystalline wax, and hard wax or derivatives thereof obtained from the Fischer Tropsch synthesis. (col. 5, 1. 45-56). This reference does not disclose applicant's formulation for the release layer nor does it contemplate the advantages which applicant has derived from such formulation. U.S. Pat. No. 2,990,311 is herein incorporated by reference.
U.S. Pat. No. 2,862,832 discloses a heat transferable decal having a release layer composed of an oxidized wax. The disclosure is directed principally to defining the type of wax found to provide suitable release of the decal from the carrier web upon application of heat. The wax disclosed in this reference is an oxidized wax obtained as the reaction product of the oxidation of hard, high melting, aliphatic, hydrocarbon waxes. The oxidized waxes are defined as the oxidation products of both natural and synthetic hydrocarbon waxes such as petroleum waxes, low molecular weight polyethylene and waxes obtained from the Fischer-Tropsch synthesis. Suitable wax may include oxidized microcrystalline wax or the esterification product of an oxidized hydrocarbon wax. The oxidized waxes are disclosed as those having melting points between about 50.degree. C. and 110.degree. C., saponification values between about 25 and 100, acid values between about 5 and 40, and penetrometer hardness (ASTM D5-52) below about 51 as measured with 100 grams for 5 seconds at 25.degree. C.
Although this reference mentions that minor amounts of certain additives such as fillers and resins may be added to the oxidized wax, the invention is clearly concerned with the use of wax as the essential component and designation of specific wax types found to give advantageous results. This reference does not disclose applicant's principal additives or applicant's combined formulation nor does it recognize or contemplate the advantages obtained from such formulation. U.S. Pat. No. 2,862,832 is herein incorporated by reference.
U.S. Pat. No. 3,616,176 discloses a heat transfer laminate of a type related to that disclosed in U.S. Pat. No. 3,616,015. In U.S. Pat. No. 3,616,176 the laminate is composed of a base sheet, with a polyamide layer covering the base sheet and a decorative ink layer covering the polyamide layer. Sufficient heat is applied to the laminate to heat the polyamide layer at or above a softening point, and the laminate is then pressed onto the surface of an article with the decorative ink layer coming into direct contact. Upon withdrawal of the heat source, the polyamide layer cools to a temperature below the softening point and the base sheet is removed. The decorative layer becomes fused or heat sealed to the article. The polyamide layer in ths disclosure functions as a release coating which allows transfer of the decorative layer onto an article and upon cooling serves as a protective coating layer over the transferred decorative layer. The use of a polyamide release coating has the principal disadvantage in that there is a significant tendency for the polyamide to form a noticeable halo around the transferred decorative layer. Also the polyamide layer even when subjected to additional processing such as post-flaming does not form sufficiently clear coating that would esthetically permit heat transfer labelling onto clear articles or bottles.
U.S. patent application Ser. No. 130,303 file date Apr. 14, 1980, commonly assigned with the present application, discloses a heat transfer label of the type illustrated in U.S. Pat. No. 3,616,015. The heat transfer label disclosed in Ser. No. 130,303 is composed of a carrier member (base sheet) overcoated in designated regions with a release layer and an ink design layer. Optionally, a barrier layer is included between the release layer and the ink layer. The release layer is typically composed of a polymerization product of a diamine with the dimer of a fatty acid. In order to reduce the halo effect of the transferred release layer over the ink design layer, the release layer is contoured in a particular manner. To further reduce the halo effect, this reference teaches that the optional barrier layer included between the release layer and ink layer, be formed of an aromatic acid-based polyester covering and overlapping the release layer by a margin.
U.S. patent application Ser. No. 146,999 file date May 6, 1980 commonly assigned with the present patent application, also discloses a heat transfer label of the type illustrated in U.S. Pat. No. 3,616,015. The heat transfer label disclosed in Ser. No. 146,999 is composed of a carrier member (base sheet) overcoated in designated regions with a release wax layer, a protective barrier layer, an ink design layer, and an adhesive layer. The protective (barrier) layer is placed preferably between the release wax layer and the ink design layer. The protective layer provides enhanced chemical resistance for the heat transfer label and permits the heat transfer label to resist distortion during the heat transfer process without sacrifice in label clarity.
Accordingly, it is an object of the present invention to provide an improved release for heat transferable substrates which permits transfer of an ink design image from a support member to a plastic or glass container.
It is an important object to provide a release which has improved optical clarity and required release and adhesive properties.
It is a further object to provide an improved release and heat transferable substrate for use in transfer of optically clear design image from a support to a clear plastic or glass container. A related object is to provide an improved optically clear release which also functions as a protective coating for the transferred image.